1. Field of Invention
This invention relates to a color image forming device for a color copier, a color facsimile or the like, which scans a color image, performs image processing on the obtained color separation signal and forms a color image.
2. Description of Related Art
Recently, the number of color print original documents have increased because of the widespread use of personal computers that deal with color printers and color images and which facilitate the creation of color images for the general user. In addition, the use of color image forming devices in color copiers and the like have become widespread, and not only the duplication of color printed original documents, color picture original documents and the like, but the re-duplication of duplicate documents by color copiers has also increased.
Many of the image processing parameters which are set for duplication comply with and provide for an assumed type of original manuscript in order to improve the color reproducibility and the gradation reproducibility. For example, menus are provided for a "printed photograph", which assumes a printed original document printed by using a general ink set, a "sensitized paper photograph", which assumes a photographic original document, and the like. When a reproduction of the duplicate copy is desired that is better than the duplicate, by selecting the type of original document, it is possible to perform correction of set gradation characteristics and color characteristics.
In the case of a "sensitized paper photograph", for example, where the reproduction characteristic is continuous gradation and not area gradation such as dotted gradation screen characteristics such as sharpness, and a natural filter characteristic can be selected because there is a degree of freedom in the screen design. In addition, it is possible to form color conversion characteristics matching the color separation characteristics of the image input device and the color material of the sensitized paper.
Meanwhile, in the case of a "printed photograph" original document, a reproduction characteristic is area gradation by a dotted screen, so the spatial filter and the screen characteristics are generally adjusted to avoid the moire effect from the interference between the sampling frequency during reading and the output reproduction screen.
The technology which changes the image processing parameters according to the type of original document are taken from prior art: for example, in Japanese Laid-Open Patent Publication No. Hei 7-276711, a color correction table is selected according to the input original document. In addition, in Japanese Patent Publication No. Hei 6-69211, revised density data of the density conversion table is re-written according to the image classification. Furthermore, a method of acquiring the image processing parameters corresponding to the original document, for example as recorded in Japanese Laid-Open Patent Publication No. Sho 60-19359 and Japanese Patent Publication No. Hei 6-100861, a set pattern, original document and the like are output one time, read and then determined by contrasting it with the original pattern and original document.
When an output original document from a certain color printer is copied again as the original document (hereafter called generation duplicate), in addition to the characteristics which should be considered as in the case of a "printed photograph" original document, it is necessary to attain in advance the mode reproduction characteristics which were used when processing and outputting the prior generation. This is because, in order to make a true reproduction of the original document, generally, the first generation copy aims for color reproduction and gradation reproduction which are completely identical to the original document. However, because of limitations in input device and output device characteristics, image processing structure and the like, a reproduction completely identical to a common original document is not possible. Accordingly, for an original document, there are numerous cases in which reproduction is carried out after making considerations such as slightly intensifying color reproduction and slightly intensified emphasis of sharpness. Also, because of differences in characteristics such as the original document paper and the copy paper, minute control is necessary for a high-lite reproduction condition. For various original document modes, such as a character original document mode and a map original document mode, for example, in a mode corresponding to a special original document, the appearance of the document copy is considered more than a true reproduction, and cases exist in which characteristics of sharpness, gradation, and the like are set in a higher shade of emphasis than the original document. If processing in this type of mode continues, the emphasized parts will become more emphasized, while the lighter parts become even lighter, resulting in a poor condition from image quality of exceedingly unbalanced characteristics.